Conventional temperature control apparatuses are commonly used in both stationary and mobile applications. Generally, these temperature control apparatuses are used to pull down the temperature in a conditioned space to a predetermined set point temperature and to maintain the temperature of the conditioned space within a range surrounding the set point temperature.
Typically, conventional temperature control apparatuses utilize conventional refrigerants (e.g., R-12, R-134(a), and the like) in a mechanical refrigeration cycle. The mechanical refrigeration cycle requires an evaporator, a condenser, and a refrigerant compressor driven by a prime mover, such as, for example, a diesel powered internal-combustion engine.
Mobile temperature control units are commonly mounted on refrigerated containers, refrigerated straight trucks, refrigerated tractor-trailer combinations, and the like, to maintain cargo, such as foods and beverages, at or near a desired set point temperature. In other applications, temperature control apparatuses can be used to condition air in a conditioned space to improve human comfort, such as, for example, in buses and passenger trains. Temperature controlled vehicles typically include an on-board dedicated mechanical temperature control apparatus for conditioning the air in the vehicle during transportation. Generally, the dedicated temperature control apparatus is also used to pre-cool the vehicle before the vehicle is loaded so that passengers and/or cargo are not exposed to temperatures which are significantly above the desired set point temperature. Because these dedicated temperature control apparatuses are incorporated in the vehicles, they are generally small and lightweight. Consequently, these dedicated temperature control apparatuses may have low cooling capacities. Relatively high cooling capacities are required to pull down a higher temperature conditioned space to the desired set point temperature in a relatively short time. For example, a conventional mechanical temperature control apparatus can take as long as six hours to cool the interior of a refrigerated trailer from an ambient outdoor temperature of 100° F. to a desired set point temperature of −20° F. During this time, the refrigerated trailer is generally parked in a lot and cannot be used to transport product until the desired set point temperature is achieved. Similarly, buses are often parked at a depot or warehouse while the on board mechanical temperature control apparatus pulls down the temperature of the air in the bus to a comfortable predetermined set point temperature.
In remote locations, such as in rural or under developed areas and on farms, electricity and diesel fuels are often not readily available. Therefore, it is often difficult to refrigerate large quantities of agricultural products until the agricultural products can be transported from the farms to processing facilities, which may be miles away. Additionally, because electricity and diesel fuel may not be readily available, the trucks and trailers that are used to transport agricultural products to the processing facilities are often not adequately refrigerated. Moreover, during loading, the trucks and trailers are frequently opened, allowing warm air to enter the trucks and trailers. Therefore, the agricultural products may be exposed to elevated temperatures for extended periods of time after being harvested. This exposure can cause spoilage and waste, contribute to the growth of harmful bacteria and parasites, and reduce the shelf life of the agricultural products.